1. Field of the Invention
The present invention is directed to an air conditioning system providing for the cross-flow mixing of a warm air flow with a cool air flow.
2. Related Technology
Air conditioning systems for the automobile sector are designed to create at least one air flow that is adapted to be conditioned according to the user's wishes, i.e. an air flow that is freely adjustable in intensity or temperature.
In order to create such an air flow, ambient air is taken by a fan and is fed into the conditioning unit of the air conditioning system after having traversed a filter. There, the ambient air intake is cooled to a defined initial temperature by means of a heat exchanger in which a liquefied refrigerant is vaporized. This initial temperature is typically less than 10° C., and often is on the order of 4° C. As the air intake is cooled down, it is also dehumidified. A cool air flow with a defined initial temperature and defined initial air humidity is thus created.
A portion of this air flow is conducted through another heat exchanger in which a heated medium, e.g., the cooling fluid of the automotive vehicle's drive unit, is circulated. Since the temperature of the coolant is substantially constant when the automotive vehicle is operating, a warm partial air flow of a substantially constant temperature is thus created. The thus provided cool and warm partial air flows are then supplied to a mixing chamber in a mix ratio that is to be controlled by suited actuator elements.
The mixing chambers of prior art air conditioning systems rely on controlled mixing of the warm and cool partial air flows supplied to the mixing chamber. This mixing is performed in such a manner that a mixing zone with a shear layer having a stable temperature profile along an axis is formed within the mixing chamber. A typical feature of these mixing chambers is that the flow paths of the supplied warm and cold partial air flows do not traverse the mixing chamber in a straight line. In graphical terms, a warmer air conditioned air flow generally does not exit the mixing chamber on the side opposite the entrance site of the warm partial air flow. As a rule, the warmer air flow created in the mixing chamber rather exits the mixing chamber at an angle of about 90° to the flow direction of the incoming warm partial air flow. If the flow path of the warmer partial air flow in the mixing chamber is understood to refer to the flow path that runs from the entrance site of the warm partial air flow to the exit site of the warmer air-conditioned air flow, the flow path of the warm partial air flow running through the mixing chamber is not straight but angled. The same applies to the flow path of the cool partial air flow. In a conventional mixing chamber, the incoming warm and cool partial air flows meet in such a manner that they strike each other at an angle and are redirected toward their respective exit sites, forming thereby a shear layer located between the redirected partial air flows. The temperature of the partial flow exiting the mixing chamber is thereby substantially determined by the arrangement of the exit ports, since it is the arrangement of the exit ports that permits to determine which spatial region of the shear layer is fed to the exit port.
This permits to adjust the temperature of the air-conditionable air flow exiting the outlet by selecting the spatial position of an outlet along this axis. It is in particular possible to provide the mixing chamber with various outlets which are arranged in different locations along said axis. It is thus possible to create a plurality of conditioned air flows of different temperatures without changing the mix ratio of the cool and warm air flows supplied. As a rule, the temperature difference between the air flows or the relationship between the temperatures of the air flows is predetermined by selecting the outlet locations from the mixing chamber.
Changing the mix ratio of the incoming warm and cool partial air flows by simultaneously actuating the corresponding actuator elements causes the temperature of all of the conditioned air flows exiting the mixing chamber to change. This means that the various air flows created are not adapted to be individually air-conditioned, but only to be commonly air-conditioned. Still, creating air flows that are not adapted to be individually air-conditioned for providing air conditioning to an automotive vehicle's interior may be advantageous since the physiological requirements placed for example on the temperature of the air flows blown into the automotive vehicle's interior are different for different parts of the human body. The lower limbs for example, especially the feet, are particularly sensitive to cold so that, here, an incoming air flow, which is warmer than the one blown into the region of the dashboard/the console, offers physiological advantages and feels pleasant to the user of the automotive vehicle.
The disadvantage of the “stratified air flow mixer concept” however is that, in order to achieve the static temperature profile mentioned, the incoming warm and cool partial air flows are usually blown from one end of the mixing chamber. This results in a strong geometrical limitation on the choice of the flow paths of the warm and cool partial air flows supplied to the mixing chamber, which in turn restricts the possibilities of construction and design.